A gas turbine engine installed as an aircraft engine comprises a compressor compressing ambient air, a combustor burning fuel together with the compressed air and a turbine for driving the compressor. The expanding combustion gases drive the turbine and also result in thrust used for propelling the aircraft.
Air breathing machines like jet engines consume large quantities of air. Air contains foreign particles in form of aerosols or larger particles which then enters the engine with the air stream. The majority of the particles will follow the gas path through the engine and exit with the exhaust gases. However, some particles have properties that cause sticking on to components in the engine's gas path. Buildup of particles changes the aerodynamic properties of the engine and more particularly reduces engine performance. Typical contaminants found in the aviation environment are pollen, insects, engine exhaust, leaking engine oil, hydrocarbons coming from industrial activities, salt coming from nearby oceans, chemicals coming from aircraft de-icing and airport ground material such as dust.
The contaminants sticking on to components in the engine gas path may cause fouling of the engine. The consequence of gas path fouling is an engine operating less efficiently than normal. With the reduction in efficiency, the engine is less economic to operate and produces higher emissions. Fouling will result in more fuel having to be burnt to achieve the same thrust as a clean engine. Further, an environmental drawback is found with the higher fuel consumption in form of increased carbon dioxide emissions. In addition, more fuel being burnt results in higher temperatures in the engine's combustor. With this also comes high temperature exposure to engine hot gas path engine components. The higher temperature exposures can dramatically shorten the life expectancy of the engine. The higher firing temperature results in increased formation of NOx which is yet another environmental drawback. In summary, the operator of a fouled engine can suffer from reduced engine lifetime, unfavorable operating economics and higher emissions. Therefore, airline operators have a strong incentive to keep their engines clean.
It has been found that the only reasonable way to combat fouling is to wash the engine. Washing can be practised by directing a water jet from something as simple as a garden hose towards the engine inlet. However, this method has limited success due to the rudimentary nature of the process. An alternative method is pumping the wash liquid through a manifold with special nozzles directed towards the engine inlet face. The manifold would be temporarily positioned near the inlet of the engine. This can include mounting the manifold on the engine cowl or on the engine shaft bullet during the wash operation. Simultaneously with spraying the washing liquid towards the engine inlet, the engine shaft is cranked such as by the use of its starter motor. The shaft rotation enhances the wash result by the mechanical movements and by forcing air with washing liquid entrained therein through the engine. This allows the wash liquid to move over greater surface area as well as enhancing liquid penetration into the interior of the engine. The method is proven successful on most gas turbine jet engines types.
A proper wash operation of a gas turbine engine can be confirmed by an observation of the wash liquid that exits the engine at the engine outlet. At the engine outlet the wash liquid has become a waste liquid. The waste liquid may leave the engine outlet as a stream of liquid pouring to the ground. Alternatively the waste liquid may be carried with the air stream as fine droplets where the air stream is the result of the rotation of the engine shaft. This air borne liquid can be carried a significant distance before falling to the ground. It is shown from actual wash operations that waste liquid will be spread on a large surface area, typically more than 20 meters downstream of the engine outlet. It is undesirable to spread waste liquid on the ground behind an engine. Thus, a method and apparatus to collect the waste liquid exiting the engine is desired.
The waste liquid exiting the engine at washing consists of the wash liquid entering the engine together with released fouling material, combustion solids, compressor and turbine coating material, and oil and fat products. The waste liquid may be hazardous. As one example, analysis of water collected from actual turbine engine washing operations have been shown to contain cadmium. The cadmium comes from compressor blade coating material released during washing operation. Cadmium is extremely environmentally sensitive and can not be allowed to be disposed to the environment. Waste liquid containing such materials will likely have to undergo treatment for separation of hazardous components before being disposed into a sewer or by other means.
Gas turbine aircraft engines can be of different types such as turbojets, turboprop, turbo-shaft and mixed or un-mixed turbofan engines. These engines cover a large performance range and may include different design details delivered by different manufacturing techniques. Aircraft types for a particular service may be offered from different aircraft manufacturers; thus the design of aircraft and engines may vary. Further, aircraft manufacturers may offer different engine options for the same aircraft type. The large combined possibility of engines on aircraft types and from different aircraft manufacturers result in a practical problem in designing a system for collecting and treating waste wash liquid that is generally applicable to most winged aircraft. U.S. Pat. No. 5,899,217 to Testman, Jr. discloses an engine wash recovery system that is limited to small, and particularly turboprop, engines as the container used in the invention is not applicable to the air flows emanating from e.g. large turbo-fan engines.
Collecting waste water from engine washing may be accomplished by hanging canvas like collectors under the engine nacelle. However, any operation resulting in anything being hooked on to an engine has the disadvantage that it may subject the engine to damage.
A system of the above described type is disclosed in International application WO 2005/121509 (owned by Gas Turbine Efficiency AB). This system comprises a liquid separating means and a collecting device for collecting waste liquid during a washing operation of an engine. It also has a treatment device for treating waste liquid collected during said washing operation. The system is provided on a mobile vehicle to service an engine with a washing operation wherever the engine may be. The vehicle comprises a chassis provided with wheels and there is a means for adjusting the position of the liquid separator and/or the liquid collector and/or the liquid storage means relative the engine.
The above discussed system may not be readily usable for types of aircraft having their exhausts located at a non-perpendicular orientation with respect to the aircraft body or being positioned centrally on the body. The system may also not be readily usable for collecting the smallest droplets in an airflow exiting the engine outlet during washing operation of an engine.